Wednesday, April 08, 2009

Scientists Use Monkeys To Discover Why Scratching Soothes the Itch

Using monkeys for their study, the scientists focused on a particular type of spinal nerve that transmits a signal from an area located near the bottom of the rib cage that travels up into the brain and causes the itching sensation. The monkeys, long-tailed macaques, were injected with a chemical to produce itching on the skin of one of their legs while they were under sedation. Electrodes were placed on their spinal nerves to record reaction and the spinal nerves responded by firing electrical signals.

The researchers then employed a hand-held metal device that simulated three monkey fingers to scratch the injected legs of the monkeys, causing a drop in the firing rate, and signaling itch relief. However, when the researchers scratched the legs of the monkeys without creating the itch sensation, the firing rate leaped, indicating that the nerves sense whether or not relief of an itch is warranted.

Giesler explained, “It’s as if there’s a little brain in there that creates this state in which scratching — which normally excites pain cells — instead inhibits them.” The same cells that register the itch also are sensitive to pain. He went on to say, “We really want to understand that, because then we think we'll understand how to relieve itch.” He also noted that it might be possible for scientists to identify the signals that prompt the nerves to respond with relief and attempt to imitate the action stimulation or with the use of drugs or through stimulation.

According to Dr. Gil Yosipovitch, a dermatologist at the Wake Forest University School of Medicine and founder of the International Forum for the Study of Itch, “It’s a very important study; itching is a major problem for millions of patients.”